Cars raise various ethical issues. They account for around a fifth of the UK's greenhouse gases, with a typical vehicle producing its own weight in CO2 for every 6,000 miles driven. Moreover, car emissions include a cocktail of noxious fumes which, in the UK alone, contributes to around 25,000 premature deaths each year.

And that's not to mention road accidents (more Brits have died on roads since 1945 than were killed in World War II) and the questionable ethical records of many oil and car companies. You can, alarmingly, watch the environmental and human costs of our driving increasing in real time at roadsafety.co.uk.

Thankfully, there are various steps we can take to reduce the harm done by our vehicles - from making changes to the way we drive to choosing greener cars and fuels.

Lower-carbon driving Even if your vehicle's a gas-guzzler, you could cut your fuel usage by as much as 30% by changing your driving practices:

·Take it steady - most cars achieve maximum fuel efficiency when travelling at speeds of 30-50 miles an hour. Above 55mph, fuel consumption goes up as much as 15% for every additional 10mph. So driving on the motorway at 60mph rather than 80mph can cut emissions and fuel costs by almost a third.

·Lighten the load - keep heavy items out of the car unless you need them - you'll typically lose 1 or 2% in efficiency for every 50kg you haul. Also keep an eye on tyre pressure: rolling resistance goes up and efficiency goes down by as much as 1% for every PSI (pound per square inch) below the recommended pressure range.

·Avoid idling - except when it's required. Idling is wasteful - and it doesn't benefit your car, except perhaps in extremely cold conditions. Even five minutes of idling can throw half a kilo of greenhouse gas into the air, and anything more than about 10 seconds of idling generates more global-warming pollution than stopping and restarting.

·Go smoothly - jack-rabbit starts and stops not only put wear and tear on your car, but they also use up fuel. Accelerate gradually and anticipate stops, starting to brake well in advance. If you have a rev counter, aim to change gear somewhere between 1,500 and 2,500 rpm.

·Cut back on the air-con - running air conditioning typically cuts down a vehicle's efficiency by a few percent. Note, though, that driving with the windows down can have the same effect, as it increasing the car's aerodynamic drag, especially at high speeds.

Greener cars Some cars are far greener (and cheaper to run) than others, so if you're in the market for a new vehicle, do some research. Unless you opt for an electric or hybrid car, the first question is diesel versus petrol.

Generally speaking, diesel cars are worse than petrol models in terms of poisonous emissions, but they're significantly more fuel-efficient and hence better in terms of global warming. As such, diesels are generally a greener choice for people living in the countryside, but city dwellers concerned about urban air quality might prefer to plump for petrol.

Whichever type you choose, it's not hard to find information about the relative greenness of the various models. The Environmental Transport Association provides emissions data, plus an overall environmental star rating, for most of the cars on the UK market.

Electric hybrids Hybrid cars, such as the Toyota Prius and Honda Insight, look and drive just like normal cars, yet their semi-electric engines are as much as twice as efficient as their straight petrol equivalents. Hybrids never need to be plugged in and charged up: the car charges its own battery when the brakes are applied or when the petrol-powered part of the engine is powering the car along at high speeds. The battery's energy is then automatically used when lower speeds are required.

The only problem is that hybrids are still quite expensive - expect to pay around 10-20% more than you would for an equivalent non-hybrid model. Also, the fuel consumption won't necessarily be lower than that of a small, super-efficient, non-hybrid diesel such as the Toyota Yaris. That said, hybrids only cost £40 a year in road tax and are exempt from the London congestion charge.

To get maximum efficiency out of a hybrid car you should accelerate briskly until you reach 30-40mph. When it's time to slow down, brake slowly at first, then increase the pressure: this ensures that the maximum energy goes into recharging the battery rather than creating heat.

Electric cars Recharged via a standard mains socket, electric cars are the greenest vehicles on four wheels. Even if charged up with electricity generated from fossil fuels, they're far more eco-friendly than petrol cars, due to their high levels of energy efficiency. Furthermore, they emit literally no harmful fumes, making them ideal for urban use.

Unfortunately, though, most electric cars can't go very fast and they need to be plugged in to recharge after a certain number of miles (between 30-200, depending on the model). Moreover, you need a parking space near a plug socket.

Currently, the only electric car widely available in the UK is the G-Wiz. Designed for two adults plus either two children or shopping, and capable of 40mph, the G-Wiz will do 40 miles on a single charge. The car costs £7,000, but you can make significant savings in fuel (a G-Wiz achieves the equivalent of 600 miles per gallon), tax (electric cars are exempt) and, in central London, parking and congestion charges (both free).

Which fuel? Even if you don't upgrade to a greener vehicle, you may want to consider what you put in your existing one. That might mean favouring certain petrol brands over others (Greenpeace is calling on consumers to boycott "climate criminal" Esso), or it might mean switching to an alternative fuel type.

If you have a petrol car, you could have it converted to run on LPG (liquid petroleum gas), which is basically propane as used in camping stoves. This can reduce CO2 output per mile by around 30% in addition to cutting poisonous emissions. Conversion costs a few thousand pounds, but once it's done you can get cheap fuel and, in London, exemption from the congestion charge.

A zero-investment alternative is to use petrol containing up to 5% bioethanol, though this isn't yet widely available in the UK and doesn't result in major emissions reductions.

If you have a diesel car, you could opt for biodiesel - made from crops rather than petroleum. If prepared from recycled vegetable oil, this is a very climate-friendly fuel. However, it can also be made from palm oil, the growing of which has led to catastrophic deforestation in south-east Asia.

After a conversion costing £500-£1,000 many diesel engines will run perfectly well on standard vegetable oil. As long as you declare what you're doing and pay the relevant tax, it's perfectly legal, too.

·This is an extract from the new Rough Guide to Ethical Living by Duncan Clark, available from bookshops for £9.99.